Catalytic reforming is a process for treating naphtha fractions of petroleum distillates to improve their octane rating by producing aromatic components and isomerizing paraffins from components present in naphtha feedstocks. Included among the hydrocarbon reactions occurring in reforming processes are: dehydrogenation of naphthenes to aromatics, dehydrocyclization of paraffins to aromatics, and hydrocracking of paraffins to lighter gases with a lower boiling point than gasoline. Hydrocracking reactions which produce light paraffin gases are not desirable as they reduce the yield of products in the gasoline range.
Natural and synthetic zeolitic crystalline aluminosilicates and borosilicates are useful as catalysts. The use of ZSM-type catalysts and processes are described in U.S. Pat. Nos. 3,546,102, 3,679,575, 4,018,711 and 3,574,092. Zeolite L is also used in reforming processes as described in U.S. Pat. Nos. 4,104,320, 4,447,316, 4,347,394 and 4,434,311.
Borosilicate zeolites are especially useful in catalytic reforming. Methods for preparing high silica content zeolites that contain framework boron are described in U.S. Pat. No. 4,269,813.
The use of intermediate pore borosilicate zeolites for catalytic reforming is described in European Patent Application No. 188,913. In this application, ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38, ZSM-48 and zeolite beta have been identified as intermediate pore borosilicate zeolites.
A method for controlling catalytic activity of large-pore boron-containing zeolites is described in European Patent Application No. 234,759.